The invention relates to a flow machine with a ceramic abradable and to a method for the manufacture of materials which can be used for the abradable.
With flow machines such as airplane engines, stationary gas turbines, turbocompressors and pumps, it is necessary for a high efficiency for a sealing gap or clearance between vane tips and housing at the periphery of a rotor bearing runner vanes to be very narrow during operation. By using an abradable on the inner surface of the housing over which the tips of the runner vanes move, it is possible to produce a minimum clearance without the runner vanes being damaged in the process. The abradables must be made of ceramic material for high operating temperatures lying above 800° C. This can be applied by means of thermal spraying process, flame spraying or atmospheric plasma spraying (APS). Porosity, and so friability, of the abradable can be produced by mixing a phase which can be burned out (polymer powder) to a ceramic spray powder. Fine particles from the surface of the abradable are released by the vane tips of the rotating rotor due to this friability.
Abradables are known from EP-A-1 111 195 and EP-A-0 935 009 which are known as structured surfaces. Ceramic abradables with non-structured surfaces are also used. The vane tips usually have to be armored in these so that they are not damaged during abrasion. (Armoring can be produced, for example, by laser remelting with the simultaneous addition of hard particles.) Released abrasion particles must be able to escape from the clearance without any significant resistance. Armoring of the vane tips can be omitted with an abradable having a suitably structured surface, since abrasion particles escape from the clearance without any damaging effect.